Isaac Hanson remained hospitalized in Texas on Thursday after suffering chest and shoulder pain following a performance earlier this week.
The family requested that no information be released on the 26-year-old singer's condition, Baylor University Medical Center spokeswoman Maria Carpenter said.
Hanson was taken to the hospital Tuesday night.
Television station KDFW reported that Hanson was diagnosed with a pulmonary embolism, which occurs when a blood clot in the extremities breaks away and travels to the lungs.
Taylor Hanson, 24, told the TV station that his brother was doing well.
Hanson, which also includes 21-year-old Zac Hanson, is best known for their 1997 hit single "MMMBop."